The manufacture of optoelectronic modules, for instance an optoelectronic transmitter (or receiver), requires that an optical fiber be properly aligned and fixed in front of the emitting (or receiving, respectively) device. A critical parameter is the transmission efficiency between the emitting (or receiving, respectively) device and the fiber. The objective is to maximize the transmission efficiency and to minimize the optical coupling losses.
The alignment of an optoelectronic device to the output (or input) optical fiber is the most critical step in the optoelectronic package manufacturing. Indeed, optical connections are highly sensitive to the relative motion between the optoelectronic device (laser, photodiode, light-emitting diode (LED), semiconductor optical amplifier (SOA), etc.) and the other optical components, which typically include a lens and a fiber, but can also include an isolator, mirrors, etc. They require extremely accurate submicrometer alignment and an attachment process that will maintain the alignment both during assembly and in the field. The techniques for locking an optical fiber within an optoelectronic package must be reproducible and reliable over time and under harsh conditions (temperature cycling and humidity). As explained below, the current techniques have all theirs drawbacks and do not provide a complete satisfactory solution to these demands.
Prior-art standard optical fiber alignment approaches fall under either active or passive alignment techniques. The former have a poor resolution of 1 or 2 μm which prevents their use in most configurations. The latter yields a final positioning accuracy of roughly 250 nm; however, it shows a post-bonding shift which is not easily controllable. In practice, the pigtailing process takes roughly 10 to 15 minutes for one fiber.
All the above techniques fail when the optoelectronic package experience large temperature changes (from −40° C. to 85° C.), either imposed by external environmental conditions or by the optoelectronic device operation itself (internally generated heat). This is especially true for packages free of thermo-electric coolers (TEC). The heat generated during device operation is not properly evacuated and yields misalignment between the optoelectronic device and the output fiber through a mismatch of thermo-mechanical properties of the coupling system (which includes the device submount, device solder, fiber solder, etc.).
Once in the field, the optical fiber connection should remain in place without need of repair. To overcome these shortcomings, The Boeing Company and MacDonnell Douglas Corporation have proposed the use of a microactuator within the package itself to enable a re-alignment of the fiber once the package is hermetically sealed. They proposed two different solutions:                a carrier movably mounted on a substrate, with the fiber permanently fixed on it (U.S. Pat. No. 5,602,955), or        the possibility of softening again the solder and moving the fiber to the optimum position before cooling down the solder (U.S. Pat. No. 6,164,837).        
The apparatus described in the aforementioned patents do not allow a complete remote actuation of the optical coupling since the module has to be taken out of the “network” to improve the optical connection.
In U.S. Pat. No. 6,280,100, a photodetector for detecting undesired light propagating in the fiber cladding is provided in the module. Optimum coupling is supposed to be found when the photodetector signal is zero. However, this optimization scheme can lead to a zero-coupling result since the optimum coupling is found on a zero-signal configuration. The processing of signals is not described.
Other types of micro XYZ stages have been proposed in E. T. Enikov and J. B. Nelson, “Three-dimensional microfabrication for a multi-degree of freedom capacitive force sensor using fibre-chip coupling”, Journal of Micromechanical engineering, 10, 492–497, 2000, or in L. Y. Lin, J. L. Shen, S. S. Lee, M. C. Wu, “Surface-Micromachined micro-XYZ stages for free-space microoptical bench”, IEEE Photon. Tech. Lett. 9, 345–347, 1997.